Certain neurons in the preoptic region and anterior hypothalamus play a significant role in thermoregulation. Not only are these neurons sensitive to their own local temperature, but in addition, many of these neurons receive afferent inputs (ultimately) from thermoreceptors in the skin and spinal cord. A model has been proposed describing how hypothalamic neurons integrate central and peripheral thermal information in order to produce appropriate thermoregulatory responses to maintain body temperature constant. In this neuronal model, it is proposed that the amount and type of afferent input going to a neuron determines the degree and range of that neuron's local thermosensitivity. The temperature range in which a neuron is sensitive is an important indication of the probable thermoregulatory function of that neuron. The objective of the proposed research is to test and improve this hypothesized model. This will be done by comparing the firing rate and thermosensitive characteristics in 1) normal, intact neurons, 2) neurons receiving a wide variety of sensory input signals, and 3) neurons whose afferent inputs have been partially removed due to lesions and blocking agents. Rabbits will be implanted with thermodes and thermocouple reentrant tubes, and single units will be studied in different areas of the hypothalamus, preoptic region and septum. Each unit will then be categorized according to its firing rate and local thermosensitivity. Statistical comparisons will then be made between the neuronal characteristics under the different afferent conditions and in the different neural areas. In addition, whole-animal thermoregulatory responses (i.e., panting, skin blood flow, and metabolism) will be studied under the same conditions as the neuronal activity. In this way, the responses of individual neurons will be compared with actual physiological responses, representing the total output of an entire neuron population.